The present application claims priority to Application No. 102 03 728.0, filed in the Federal Republic of Germany on Jan. 30, 2002, which is expressly incorporated herein in its entirety by reference thereto.
The present invention relates to systems for exhaust-gas aftertreatment used in internal combustion engines, e.g., of motor vehicles, and relates to a method, a circuit and a control device to protect against an, e.g., inadvertent, installation exchange of exhaust-gas sensors in such a device.
Devices for exhaust-gas aftertreatment in motor vehicles are widely conventional. For instance, a lambda control in conjunction with a catalytic converter is currently an effective exhaust-gas treatment method for the spark-ignition engine. In interaction with currently available ignition systems and injection systems, very low exhaust-gas values may be achieved. In most countries, limit values for the engine exhaust gas are even mandated by law.
Especially effective is the use of a three-way catalytic converter, or selective catalytic converter. This type of catalytic converter is able to break down up to more than 98% of hydrocarbons, carbon monoxide and nitrogen provided the engine is operated within a range of approximately 1% around the stoichiometric air-fuel ratio, with lambda=1. In this context, lambda specifies the degree to which the actually present air-fuel mixture deviates from the value lambda=1, which corresponds to a mass ratio of 14.7 kg air to 1 kg of gasoline that is theoretically required for complete combustion, i.e., lambda is the quotient of the supplied air mass and the theoretical air requirement.
As a general principle, lambda control measures the respective exhaust gas and, on the basis of the measuring result, immediately corrects the supplied fuel quantity with the aid of the injection system, for instance. Used as sensors are either so-called lambda voltage-jump sensors (two-step sensors), which have a voltage jump at precisely lambda=1 and in this manner supply a signal that indicates whether the mixture is richer or leaner than lambda=1. In addition, lambda sensors providing a continuous lambda signal in the range of lambda=1 are used, which, as in the case of lambda voltage-jump sensors, indicates whether the mixture is richer or leaner than lambda=1. As conventional, the action of all sensors is based on the principle of a galvanic oxygen-concentration cell including a solid-state electrolyte (mostly zirconium-dioxide).
So-called xe2x80x9cdividedxe2x80x9d catalytic-converter systems, which are made up of a precatalyst (precat) and a main catalyst (main-cat), are often used for the mentioned catalysis. A common construction type is the cat system shown in FIG. 1, which works according to a 3-sensor principle to achieve very strict exhaust-gas limit values. These cat systems include a detection in case the two LSF sensors disposed before and after the main cat have been exchanged. However, while this detection outputs an error message by generating an electronic error bit if sensors have been exchanged in error during installation, it does not allow any interventions to compensate for such an exchange.
Therefore, the described systems for exhaust-gas aftertreatment have the disadvantage that the error message is the sole response to an exchange of the mentioned sensors or their plug connections, the cat system, however, being unable to continue fulfilling its function.
It is an object of the present invention to provide a method, a circuit and a control unit for operating a device for exhaust-gas aftertreatment in an internal combustion engine, especially of a motor vehicle, which may allow a detection of a possible installation exchange of exhaust sensors, while simultaneously permitting a correction of the occurred exchange of these sensors, so that the device for exhaust-gas aftertreatment is able to continue functioning without interruption.
The above and other beneficial objects of the present invention are achieved by providing a method, a circuit and a control unit as described herein.
The present invention is based on providing an electronic exchange protection, where the control device, if an exchange is detected, implements a switch-over, internally to the control device, among the signals of the exchanged measuring sensors. An exchange bit provided by a diagnostic unit may be used.
The present invention may thus permit a reliable electronic exchange protection in an engine control unit; instead of the cat system reacting with an error message, it continues operating in a fail-safe manner. The exchange detection not only detects an exchange of the two LSF sensors, but also compensates for the exchange, so that the engine control unit and the engine are able to continue operating without interference and interruption in their function. The robustness of the cat control is increased as is the general every-day usefulness and quality of the cat system. Moreover, the present invention may save a mechanical protection against polarity reversal, for instance by terminal coding.
The method according to the present invention may be implemented by a control program loaded into the engine control unit, thus avoiding expensive hardware modifications at the engine control unit or the cat system.